Either there is a nasty bug in that package, or something is very wrong with your build environment. That error indicates that the test scripts, which are supposed to be run under special settings so they pick up the freshly-built extension, are not finding the module.

The package was extracted from PDL, which needed sub-packages to make a dummy build rather than terminate the configure process. That dummy-build behaviour led to what was reported here, which is the false appearance of successful installation. That behaviour has just been removed, and that will be reflected in the upcoming PDL::Graphics::PLplot 0.77.

./cpanm -L PDL::Graphics::PLplot; I tried force as well. Description: Ubuntu 16.04.7 LTS

Hi newperldeveloper,

The PDL::Graphics::PLplot distro is cunningly designed to play tricks. Here's what I get on Ubuntu-18.04, perl-5.32.0:

$ cpanm -i PDL::Graphics::PLplot
--> Working on PDL::Graphics::PLplot
Fetching http://www.cpan.org/authors/id/D/DH/DHUNT/PDL-Graphics-PLplot
+-0.74.tar.gz ... OK
Configuring PDL-Graphics-PLplot-0.74 ... OK
Building and testing PDL-Graphics-PLplot-0.74 ... OK
Successfully installed PDL-Graphics-PLplot-0.74
1 distribution installed
$
[download]

But then:

$ perl -MPDL::Graphics::PLplot -le 'print "ok";'
Can't locate PDL/Graphics/PLplot.pm in @INC (you may need to install t
+he PDL::Graphics::PLplot module) (@INC contains: /home/sisyphus/perl-
+5.32.0-d/lib/site_perl/5.32.0/x86_64-linux /home/sisyphus/perl-5.32.0
+-d/lib/site_perl/5.32.0 /home/sisyphus/perl-5.32.0-d/lib/5.32.0/x86_6
+4-linux /home/sisyphus/perl-5.32.0-d/lib/5.32.0).
BEGIN failed--compilation aborted.
[download]

Turns out that I don't have the plplot library installed.
The PDL-Graphics-PLplot distro is designed to fool the cpan and cpanm utilities into thinking that the build was a success, even when it failed.
The cpan utility makes things a little more apparent:

$ cpan -i PDL::Graphics::PLplot
Loading internal logger. Log::Log4perl recommended for better logging
Reading '/home/sisyphus/.cpan/Metadata'
  Database was generated on Thu, 20 Aug 2020 00:17:03 GMT
Running install for module 'PDL::Graphics::PLplot'
Checksum for /home/sisyphus/.cpan/sources/authors/id/D/DH/DHUNT/PDL-Gr
+aphics-PLplot-0.74.tar.gz ok
'YAML' not installed, will not store persistent state
Configuring D/DH/DHUNT/PDL-Graphics-PLplot-0.74.tar.gz with Makefile.P
+L
PDL is installed

Checking PDL::Graphics::PLplot...
Searching for libplplot.so library.
Searching for libplplotd.so library.
Cannot find plplot library (libplplotd.so), skipping PDL::Graphics::PL
+plot

      Not building PDL::Graphics::PLplot


Cannot find plplot library (libplplotd.so), skipping PDL::Graphics::PL
+plot      Not building PDL::Graphics::PLplot
Checking if your kit is complete...
Looks good
  DHUNT/PDL-Graphics-PLplot-0.74.tar.gz
  /home/sisyphus/perl-5.32.0-d/bin/perl Makefile.PL -- OK
Running make for D/DH/DHUNT/PDL-Graphics-PLplot-0.74.tar.gz
Could not read metadata file. Falling back to other methods to determi
+ne prerequisites
make: Nothing to be done for 'all'.
  DHUNT/PDL-Graphics-PLplot-0.74.tar.gz
  /usr/bin/make -- OK
The current configuration of allow_installing_outdated_dists is 'ask/y
+es', but for this option we would need 'CPAN::DistnameInfo' installed
+. Please install 'CPAN::DistnameInfo' as soon as possible. As long as
+ we are not equipped with 'CPAN::DistnameInfo' this option does not t
+ake effect
Running make test for DHUNT/PDL-Graphics-PLplot-0.74.tar.gz
make: Nothing to be done for 'test'.
  DHUNT/PDL-Graphics-PLplot-0.74.tar.gz
  /usr/bin/make test -- OK
Running make install for DHUNT/PDL-Graphics-PLplot-0.74.tar.gz
make: Nothing to be done for 'install'.
  DHUNT/PDL-Graphics-PLplot-0.74.tar.gz
  /usr/bin/make install  -- OK
[download]

See ? Everything went fine, including /usr/bin/make install ;-)

So, I'm thinking that you, too, might not have the plplot library installed.
If that's not the case, let me know how I can get apt-get to install the plplot library on Ubuntu and I'll investigate your problem further.

Cheers,
Rob